Probing local electron temperature in graphene with scanning tunneling spectroscopy and potentiometry

Understanding heat dissipation at the nanoscale is essential for constructing efficient electronic devices. Although state-of-the-art local thermometry techniques can achieve sub-kelvin temperature resolution with sub-100nm spatial precision, most techniques probe the lattice temperature as opposed to the electron temperature. In materials like graphene, where electron-phonon coupling is exceptionally weak, the electrons can reach temperatures that differ significantly from that of the lattice temperature. To probe these nonequilibrium effects in monolayer graphene, we use a scanning tunneling microscope tip as a thermometer, where a thermoelectric voltage is measured between the sample and the tip. By heating the sample by either applying current or heating it through Ti/Au heaters, we distinguish between thermovoltages generated by electrons that are coupled and decoupled from the lattice. For current-biased measurements, we use this technique to probe the temperature profile across the sample under different doping conditions. We also show how this technique can be used to probe how the Seebeck coefficient of the graphene varies locally.